Cholesteric liquid crystalline film, method for production thereof and circularly polarized light reflecting film, two wavelength region reflection type reflecting film

ABSTRACT

A cholesteric liquid crystal film of the invention consist of a single layer, which is a cholesteric liquid crystal film, formed by applying a liquid crystal mixture containing a polymerizable mesogen compound (A) and a polymerizable chiral agent (B) to an alignment substrate, and applying ultraviolet irradiation to the mixture, wherein a cholesteric liquid crystal film has at least two independent selective reflection wavelength bands. The cholesteric liquid crystal film can be prepared by a simple and easy procedure.

TECHNICAL FIELD

The invention relates to a cholesteric liquid crystal film and a methodof producing the same. The cholesteric liquid crystal film of theinvention has at least two independent selective reflection wavelengthbands and is useful as a circularly-polarized-light-reflecting plate (acircular polarization type reflective polarizer). A laminate of thecircularly-polarized-light-reflecting plates can be used as a reflectingfilm for specifically reflecting light in two specific wavelengthranges. For example, if the two specific wavelength ranges exist in anultraviolet wavelength range and an infrared wavelength range,respectively, it will be useful as a film for eye protection. Such afilm is preferably used for eyeglasses such as sunglasses and protectiveglasses for laser working, window-glasses of vehicles such asautomobiles, and windowpanes of buildings. If the two specificwavelength ranges exist in the visible wavelength range, it willpreferably be used as a complementary color filter or the like forliquid crystal displays.

BACKGROUND ART

A cholesteric liquid crystal having a circularly polarized lightseparating function has a selective reflection characteristic reflectingonly circularly polarized light having a direction thereof coincidingwith a helical rotation direction of the liquid crystal and a wavelengthequal to a helical pitch length of the liquid crystal. With thisselective reflection characteristic used, only a specific circularlypolarizing light of natural light in a given wavelength band istransmission-separated and the other light components are reflected andrecycled, thereby enabling a circularly-polarized-light-reflecting filmwith a high efficiency to be manufactured.

Two types of circularly-polarized-light-reflecting films that aresubstantially the same in selective reflection wavelength band andopposite in the rotation direction of the cholesteric spiral may belaminated so as to function as a reflecting film. Two types ofcircularly-polarized-light-reflecting films that are substantially thesame in selective reflection wavelength band and same in the helicalrotation direction of the cholesteric spiral may also be laminated witha half-wave plate (λ/2 plate) sandwiched therebetween to form a similarreflecting film.

There has been, usually, difficulty in covering all the range of visiblelight, since a selective reflection characteristic of a cholestericliquid crystal is restricted to only a specific wavelength band. Aselective reflection wavelength bandwidth. Δλ is expressed by followingformula:Δλ=2λ·(n _(e) −n _(o))/(n _(e) +n _(o))

where n_(o): ordinary light refractive index of a cholesteric liquidcrystal molecule, n_(e): extraordinary light refractive index of thecholesteric liquid crystal molecule, and λ: central wavelength inselective reflection.

The selective reflection wavelength bandwidth Δλ depends on a molecularstructure of the cholesteric liquid crystal itself. According to theabove formula, if (n_(e)−n_(o)) is larger, a selective reflectionwavelength bandwidth Δλ can be broader, while (n_(e)−n_(o)) is usually0.3 or less. With this value being larger, other functions as a liquidcrystal (such as alignment characteristic, a liquid crystal temperatureor the like) becomes insufficient, causing its practical use to bedifficult. Therefore, a selective reflection wavelength bandwidth a hasbeen actually about 150 nm at highest. A cholesteric liquid crystalavailable in practical aspect has had a selective reflection wavelengthbandwidth Δλ only in the range of about 30 to 100 nm in many cases.

A selective reflection central wavelength λ is given by the followingformula:λ=(n _(e) +n _(o))P/2

where P: helical pitch length required for one helical turn ofcholesteric liquid crystal.

With a given pitch length, a selective reflection central wavelength λdepends on an average refractive index and a pitch length of a liquidcrystal molecule.

Conventionally, therefore, different cholesteric liquid crystal layershaving different central wavelengths for selective reflection arelaminated for the purpose of freely controlling thereflection/transmission properties for any different reflectionwavelength bands.

For the purpose of cutting off ultraviolet and infrared rays harmful tothe eyes in the outdoors, for example, spectacles should have protectionfilters capable of selectively reflecting light in an ultravioletwavelength range and an infrared wavelength range. Such protectionfilters for spectacles need a laminate of different cholesteric liquidcrystal films having at least two central wavelengths for selectivereflection in an ultraviolet wavelength range and an infrared wavelengthrange. As mentioned above, the reflecting-film function requires atleast another pair of the same cholesteric liquid crystal films. Thus,the protection filter for spectacles as mentioned above needs at leastfour layers of the cholesteric liquid crystal or at least five layersincluding the cholesteric liquid crystal layers and a half-wave platesandwiched therebetween.

A variety of methods are proposed in which a cholesteric liquid crystalpolymer is used to form a cholesteric liquid crystal layer (a selectivereflection layer) with a modified band. However, all of suchconventional methods are for broadening the band of the selectivereflection layer and cannot produce a single cholesteric liquid crystallayer having at least two independent selective reflection wavelengthbands.

For example, a method is proposed in which the band of a cholestericliquid crystal layer is broadened using inhibition by oxygen (JapanesePatent Application Laid-Open No. 2002-286935). A method is also proposedwhich includes performing two-stage exposure to light and annealing in adark place to promote the mass transfer (European Patent Publication No.0885945). In all the methods disclosed in these patent applications,however, the selective reflection wavelength band of the cholestericliquid-crystal is only broadened after a reaction, and no phenomenon ofpeak division is caused for the selective reflection wavelength, andthus independent selective reflection wavelength bands are not produced.

For example, a certain cholesteric liquid crystal layer has two peaks atselective reflection wavelengths before broadband-forming treatment isperformed (U.S. Pat. No. 6,417,902). However, this patent literaturerelates to a process of multilayer coating of liquid crystal layershaving different components for combination of peaks. This process needsthe production of a plurality of liquid crystal layers and iscomplicated.

Also proposed is a liquid crystal layer having cholesteric pitchesnonlinearly varying in the thickness direction and a method of producingthe same (the brochure of International Publication No. 98/20090). Inthis patent document, however, the nonlinear variation in pitch iscontinuous and does not produce at least two independent selectivereflection wavelength bands.

The conventional known methods for producing at least two selectivereflection wavelength bands only include methods of applying andstacking at least two types of cholesteric liquid crystal layers,methods of laminating at least two types of cholesteric liquid crystallayers, and methods of forming a mixture-containing film by pulverizingat least two types of liquid crystal thin films and mixing them. All ofthe conventional methods need at least twocholesteric-liquid-crystal-layer-forming steps.

Interference filters formed by vapor-deposition of inorganic materialsare known as optical materials (polarized-light-reflecting films)similar to the cholesteric liquid crystal layer. However, the equipmentfor manufacturing the interference filters by vacuum deposition methodis expensive, and more than a dozen to twenty layers should be laminatedto form an interference filter. Therefore, the cost of the interferencefilter must be high. Similarly known is a stretched laminate of resinthin films having different refractive indices, such as DBEF, ESR andGBO multilayer films manufactured by 3M. Laminating many layers andprecision stretching are also necessary for the production of thesefilms.

DISCLOSURE OF INVENTION

It is an object of the invention to provide a cholesteric liquid crystalfilm that can be easily produced and has at least two independentselective reflection wavelength bands and to provide a method ofproducing the same.

It is another object of the invention to provide acircularly-polarized-light-reflecting plate using the cholesteric liquidcrystal film, a reflecting film using thecircularly-polarized-light-reflecting film, and a variety of opticalproducts using the reflecting film.

In order to solve the above problems, the inventors have made activeinvestigations and finally found that the cholesteric liquid crystalfilm and the method of producing the same as described below can achievethe above objects, in completing the invention. Thus, the invention isas follows:

1. A cholesteric liquid crystal film; consisting of a single layer,which is a cholesteric liquid crystal film, formed by applying a liquidcrystal mixture containing a polymerizable mesogen compound (A) and apolymerizable chiral agent (B) to an alignment substrate, and applyingultraviolet irradiation to the mixture, wherein

-   -   the cholesteric liquid crystal film has at least two independent        selective reflection wavelength bands.

2. The cholesteric liquid crystal film according to the above-mentioned1, wherein the independent selective reflection wavelength bands havecentral wavelengths for selective reflection in an ultravioletwavelength range and an infrared wavelength range, respectively.

3. The cholesteric liquid crystal film according to the above-mentioned1 or 2, wherein a reaction rate of the polymerizable mesogen compound(A) and the polymerizable chiral agent (B) is different, respectively.

4. The cholesteric liquid crystal film according to any one of theabove-mentioned 1 to 3, wherein the number of polymerizable functionalgroups in the polymerizable chiral agent (B) is larger than those in thepolymerizable mesogen compound (A).

5. A method of producing the cholesteric liquid crystal film accordingto any one of the above-mentioned 1 to 4, comprising the steps of:

-   -   applying a liquid crystal mixture containing (A) a polymerizable        mesogen compound and (B) a polymerizable chiral agent to an        alignment substrate; and    -   applying ultraviolet irradiation to the liquid crystal mixture        from the alignment substrate side in such a state that the        mixture is in contact with an oxygen-containing gas to        polymerize and cure the mixture.

6. The method according to the above-mentioned 5, wherein the step ofapplying ultraviolet irradiation to polymerize and cure the mixture isperformed at a temperature of 20° C. or more.

7. The method according to the above-mentioned 5, wherein, anultraviolet irradiation temperature at a later stage in the step ofapplying ultraviolet irradiation to polymerize and cure is controlledhigher than that at an earlier stage.

8. A two-wavelength-range reflection typecircularly-polarized-light-reflecting film, comprising the cholestericliquid crystal film according to any one of the above-mentioned 1 to 4.

9. A reflecting film capable of covering two wavelength ranges,comprising:

-   -   a laminate of two pieces of the        circularly-polarized-light-reflecting film according to the        above-mentioned 8, wherein the two pieces of the        circularly-polarized-light-reflecting film have substantially        the same selective reflection wavelength bands and are opposite        in cholesteric twist direction.

10. A reflecting film capable of covering two wavelength-ranges,comprising:

-   -   a laminate of a half-wave plate sandwiched between two pieces of        the circularly-polarized-light-reflecting film according to the        above-mentioned 8, wherein the two pieces of the        circularly-polarized-light-reflecting film have substantially        the same selective reflection wavelength bands and are same in        cholesteric twist direction.

11. The reflecting film according to the above-mentioned 10, thehalf-wave plate is a broadband half-wave plate comprising a laminate ofat least two different retardation plates.

12. An eye protecting film, comprising the reflecting film capable ofcovering two wavelength-ranges according to any one of theabove-mentioned 9 to 11.

13. An eye protecting plate, comprising:

-   -   a transparent supporting substrate; and    -   the eye protecting film according to the above-mentioned 12        which is bonded to the substrate.

14. A transparent viewing member, comprising the eye protecting filmaccording to the above-mentioned 12 or the eye protecting plateaccording to the above-mentioned 13.

15. A complementary color filter, comprising the reflecting filmaccording to any one of the above-mentioned 8 to 11.

16. A liquid crystal display, comprising the complementary color filteraccording to the above-mentioned 15.

(Functions and Effects)

The cholesteric liquid crystal film of the invention is a single layerfilm having at least two independent selective reflection wavelengthbands. The independent selective reflection wavelength bands can beselected depending on the purpose of use. The independent selectivereflection wavelength bands each preferably have a width of about 20 toabout 200 nm. The width of each selective reflection wavelength band maybe measured by the method as shown in Examples.

For example, the cholesteric liquid crystal film is produced by aprocess including the steps of applying, to an alignment substrate, aliquid crystal mixture containing (A) a polymerizable mesogen compoundand (B) a polymerizable chiral agent; and applying ultravioletirradiation from the alignment substrate side in the presence of oxygenfor inhibiting polymerization. Thus, the cholesteric liquid-crystal filmhaving any two or more selective reflection wavelength bands can beobtained with a reduced number of layers, a reduced number of processesand a reduced cost, as compared with the conventional methods.

The method of producing the cholesteric liquid crystal film according tothe invention uses the difference in the rate of polymerization betweenthe uncovered face of the cholesteric liquid crystal and thesubstrate-covered face of it, which is caused by oxygen-inducedinhibition as described in Japanese Patent Application No. 2001-339632.In this method, the exposure to light is performed in the direction fromthe substrate face side to the liquid crystal so that the difference inthe rate of polymerization can be significantly increased and that thecomposition ratio of the cholesteric liquid crystal mixture can vary inthe thickness direction. Therefore, this method is further developedfrom a method of making a difference in the pitch length of acholesteric liquid crystal layer between the uncovered face of thecholesteric liquid crystal and both sides of a substrate.

In the invention, cholesteric liquid crystal materials different inreaction rate are used and heated under the polymerization conditionsfor band broadening as described in Japanese Patent Application No.2001-339632 so that the difference in mass-transfer speed between theliquid crystal materials allows the production of at least twoextremely-separated discontinuous pitch lengths in the cholestericliquid crystal layer.

According to the basic mechanism, the selective reflection wavelengthband of the cholesteric liquid crystal produced by the initialpolymerization is set at a value determined by the liquid crystalcomposition before the polymerization, while the polymerization andheating promote the mass transfer of the liquid crystal composition sothat another independent selective reflection wavelength band isgenerated in a different wavelength range.

A mixture of a polymerizable mesogen compound (A) and a polymerizablechiral agent (B) is used as the cholesteric liquid crystal material.When the reactivity and reaction rate of the polymerizable mesogencompound (A) are lower than those of the polymerizable chiral agent (B),the polymerization is started so as to produce a selective reflectionwavelength determined by the initial blend ratio, but the rate ofconsumption of the polymerizable chiral agent (B) is higher so that thepolymerizable mesogen compound (A) can be left as the polymerizationproceeds and that the monomer ratio of the remaining composition can bedifferent from the initial ratio. In this process, the monomer transferspeed may be controlled by the control of the heating temperature sothat the blend ratio of the polymerizable mesogen compound (A) to thepolymerizable chiral agent (B) can be controlled during the later stageof the polymerization. In this case, the most part of the polymerizablechiral agent (B) is consumed by a certain time in the latter part of thepolymerization, and under such conditions, namely under thepolymerizable mesogen compound (A) rich conditions, the polymerizationis completed, so that the layer cured in the latter part of thepolymerization can have a weak twist and have a selective reflectionwavelength band at a position significantly shifted to the longwavelength side. Thus, the single layer coating of the liquid crystalmixture containing the polymerizable mesogen compound (A) and thepolymerizable chiral agent (B) and the single ultraviolet irradiation tothe mixture allow the production of regions having different pitches inthe direction of the thickness of the formed cholesteric liquid crystallayer so that the cholesteric liquid crystal film having at least twoselective reflection wavelength bands can be produced.

In the liquid crystal temperature environment, the environmentaltemperature for the ultraviolet irradiation may be increased for thepurpose of increasing the mass-transfer speed so that the single layercoating can form a similar cholesteric liquid crystal film having atleast two selective reflection wavelength bands. In this case, theintensity of the ultraviolet irradiation may also be controlled, whilethe environmental temperature is increased during the ultravioletirradiation.

The relationship between the reaction rates of the polymerizable mesogencompound (A) and the polymerizable chiral agent (B) may be varied sothat the formed film structure can be opposite to the above or the spaceof the selective reflection wavelength bands or the size of the peak ateach central wavelength for selective reflection can be controlled.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a reflectance spectrum of a cholesteric liquid crystal filmmanufactured in Example 1.

FIG. 2 is a reflectance spectrum of a cholesteric liquid crystal filmmanufactured in Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

A cholesteric liquid crystal film of the present invention is obtainedby ultraviolet polymerizing a liquid crystal mixture containing apolymerizable mesogen compound (A) and a polymerizable chiral agent (B).

The polymerizable mesogen compound (A) and the polymerizable chiralagent (B) for use preferably have different reaction rates. Typically,the more the number of the polymerizable functional groups, the higherthe reaction rate. In order to prepare the liquid crystal mixture inwhich the reaction rate of the polymerizable mesogen compound (A) islower than that of the polymerizable chiral agent (B), therefore, thenumber of the polymerizable functional groups of the polymerizablechiral agent (B) may be larger than those of the polymerizable mesogencompound (A) in the combination.

A polymerizable mesogen compound (A) preferably has at least onepolymerizable functional group and in addition, a mesogen groupcontaining a ring unit and others. As polymerizable functional groups,exemplified are an acryloyl group, a methacryloyl group, an epoxy group,a vinyl ether group and others, among which preferable are an acryloylgroup and a methacryloyl group. Using a compound having at least twopolymerizable functional groups, a crosslinked structure can also beintroduced to increase the durability. Examples of the cyclic unit forthe mesogen group include a biphenyl unit, a phenylbenzoate unit, aphenylcyclohexane unit, an azoxybenzene unit, an azomethine unit, anazobenzene unit, a phenylpyrimidine unit, a diphenylacetylene unit, adiphenylbenzoate unit, a bicyclohexane unit, a cyclohexylbenzene unit,and a terphenyl unit. The terminal of each of these cyclic units mayhave a substituent such as cyano group, alkyl group, alkoxyl group, andhalogen group. The mesogen group may be bonded via a spacer moiety forimparting flexibility. Examples of the spacer moiety include apolymethylene chain and a polyoxymethylene chain. The number of therepeating structural units forming the spacer moiety is properlydetermined depending on the chemical structure of the mesogen moiety.For example, the number of the repeating units in a polymethylene chainis from 0 to 20, preferably from 2 to 12, and the number of those in apolyoxymethylene chain is from 0 to 10, preferably from 1 to 3.

As a polymerizable mesogen compound (A) having at least onepolymerizable functional group, as described above, is a compoundrepresented by the following general formula (1):

wherein R₁ represents a hydrogen atom or a methyl group, and n is aninteger of 1 to 5.

As concrete examples of the polymerizable mesogen compound (A) having atleast one polymerizable functional group, exemplified are the compoundsrepresented by following polymerizable mesogen compound (1) to (4):

For example, a compound having at least one polymerizable functionalgroup and an optically-active group is preferably used as thepolymerizable chiral agent (B). The polymerizable functional group maybe any of the above functional groups. If the polymerizable mesogencompound (A) has one polymerizable functional group, the polymerizablechiral agent (B) should preferably have two or more polymerizablefunctional groups.

For example, the polymerizable chiral agent (B) having at least twopolymerizable functional groups may be the compound represented by thegeneral formula (2):

wherein R₂ and R₃ each represent a hydrogen atom or methyl group, R₄ andR₅ each represent an optionally substituted alkylene of 1 to 12 carbonatoms, and 1 and m each independently represent an integer of 1 to 3.

As a polymerizable chiral agent (B), exemplified is LC756 manufacturedby BASF Ltd.

A mixing amount of a polymerizable chiral agent (B) is preferably in therange of about from to 20 parts by weight and more preferably in therange of from 3 to 7 parts by weight relative to 100 parts by weight ofa total amount of a polymerizable mesogen compound (A) and thepolymerizable chiral agent (B). A helical twist power (HTP) iscontrolled by a ratio of a polymerizable mesogen compound (A) and apolymerizable chiral agent (B). By adjusting the proportion within therange, a reflection band can be selected so that a reflectance spectrumof an obtained cholesteric liquid crystal film can cover all the rangeof visible light.

The liquid crystal mixture usually contains photopolymerizationinitiators (C). Any kind of photopolymerization initiators (c), can beemployed without imposing any specific limitation thereon. Exemplifiedare IRGACURE-184, IRGACURE 907, IRGACURE 369, IRGACURE 651, IRGACURE748, IRGACURE 814, Darocure 1173, Darocure 4205 and others manufacturedby Ciba Specialty Chemicals Inc. And LucirinTPO manufactured by BASFLTD. is preferably used. A mixing amount of a photopolymerizationinitiator is preferably in the range of about from 0.01 to 10 parts byweight and more preferably in the range of from 0.05 to 5 parts byweight relative to 100 parts by weight of a total amount of apolymerizable mesogen compound (A) and a polymerizable chiral agent (B).Although the necessary amount of the photopolymerization initiator tendsto increase under air atmosphere, the desired object can be achievedusing Irgacure 369 or Irgacure 907 in an amount of about 3 to about 5parts by weight.

The liquid crystal mixture may contain an additive such as a surfactantfor smoothing the surface to be coated the amount of the surfactant orthe like may be set depending on the coating ability of liquid crystalmixture and is generally at most about 0.1 part by weight, preferablyfrom about 0.01 to about 0.1 part by weight, based on 100 parts byweight of the total amount of the polymerizable mesogen compound (A) andthe polymerizable chiral agent (B). For example, Fluorad 171manufactured by 3M LTD., Zonyl Fsn manufactured by DuPont LTD., or BYK361 manufactured by Bigchemi Japan Company LTD. is preferably used asthe additive. Any of these additives may be properly selected dependingon the type of the liquid crystal mixture, the blend properties or thelike.

The mixture may contain an ultraviolet absorbing agent for broadeningthe band width of the resulting cholesteric liquid crystal film so thatvariations in the intensity of exposure to ultraviolet irradiation canbe greater in the thickness direction. The same effect can be producedusing a photopolymerization initiator having a large molar absorptioncoefficient.

The mixture may be used in the form of a solution. Examples of thesolvent for use in the preparation of the solution generally includehalogenated hydrocarbons such as chloroform, dichloromethane,dichloroethane, tetrachloroethane, trichloroethylene,tetrachloroethylene, and chlorobenzene; phenols such as phenol andpara-chlorophenol; aromatic hydrocarbons such as benzene, toluene,xylene, methoxybenzene, and 1,2-dimethoxybenzene; and other solventssuch as acetone, methyl ethyl ketone, ethyl acetate, tert-butyl alcohol,glycerol, ethylene glycol, triethylene glycol, ethylene glycolmonomethylether, diethylene glycol dimethyl ether, ethylcellosolve,butylcellosolve, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine,triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetamide,dimethyl sulfoxide, acetonitrile, butyronitrile, carbon disulfide,cyclopentanone, and cyclohexanone. Preferred solvents for use hereininclude, but are not limited to, methyl ethyl ketone, cyclohexanone andcyclopentanone. The concentration of the solution depends on thesolubility of the thermotropic liquid crystal compound and the thicknessof the cholesteric liquid crystal film to be finally produced and thuscannot be uniquely defined but is generally preferably from about 3 toabout 50% by weight.

According to the invention, the method of producing the broadbandcholesteric liquid crystal film includes the steps of applying theliquid crystal mixture to an alignment substrate andapplying-ultraviolet irradiation to the liquid crystal mixture topolymerize and cure the mixture.

As alignment substrates, there can be adopted conventionally knownmembers as ones. Exemplified are: a rubbing film obtained by subjectinga thin film made of polyimide, polyvinyl alcohol or thelike formed on asubstrate to a rubbing treatment with rayon cloth; an obliquelydeposition film; optically oriented film obtained by illuminating apolymer having photocrosslinking group such as cynnamate, azobenzene orthe like or a polyimide with polarized ultra-violet; and a stretchedfilm and others. Orientation can be implemented by application of amagnetic field, an electric field and a shearing stress.

The substrate may be of any type but is preferably made of a materialhaving a high transmittance because the radiation (ultraviolet light) isirradiated from the substrate side in the method. For example, thesubstrate should have a transmittance of at least 10%, preferably of atleast 20%, in the ultraviolet range from 200 nm to 400 nm, preferably inthe ultraviolet range from 300 nm to 400 nm. More specifically, thesubstrate is preferably a plastic film with a transmittance of at least10%, more preferably of at least 20%, for ultraviolet irradiation with awavelength of 365 nm. The transmittance may be a value measured by meansof U-4100 Spectrophotometer manufactured by Hitachi Ltd.

The substrate may comprise a plastic film, glass or a quartz sheet.Examples of the plastic for the film include polyethylene terephthalate,polyethylene naphthalate (PEN), polyvinyl alcohol (PVA), polycarbonate(PC), triacetylcellulose (TAC), polyimide, polyarylate, polycarbonate,polysulfone, and polyethersulfone. Specific examples thereof includeMelinex (PET) manufactured by ICI. Corporation, Lumirror (PET)manufactured by Toray Industries, Inc., Diafoil (PET) manufactured byMitsubishi Polyester Film Corp., and Mylar (PET) manufactured by TeijinDuPont Films Limited.

The substrate may be used with the cholesteric liquid crystal layerattached thereto or may be separated and removed from the cholestericliquid crystal layer. The substrate for use with the liquid crystalattached thereto preferably comprises a material whose retardation valueis sufficiently small for practical use. Preferred examples for use insuch a case include triacetylcellulose films manufactured by Fuji PhotoFilm Co., Ltd. (T-TAC, TD-TAC and UZ-TAC), ARTON manufactured by JSRCorporation, Zeonex and Zeonea films manufactured by Nippon Zeon Co.,Ltd., and unstretched PC films. Examples thereof also include polymerfilms as disclosed in Japanese Patent Application Laid-Open No.2001-343529 (WO01/37007) and a resin composition that contains (A) athermoplastic resin having a side chain of a substituted and/orunsubstituted imide group and (B) a thermoplastic resin having a sidechain of substituted and/or unsubstituted phenyl and nitrile groups.Specific examples include a film of a resin composition containing analternating copolymer of isobutylene and N-methylmaleimide and anacrylonitrile-styrene copolymer. The film may be produced by mixing andextruding the resin composition.

The substrate for use with the liquid crystal attached theretopreferably comprises a material that is not decomposed, degraded oryellowed when exposed to ultraviolet irradiation. For example, thesubstrate may contain a light stabilizer so that the desired object canbe achieved. The light stabilizer is preferably Tinuvin 120 or 144manufactured by Ciba Specialty Chemicals Inc. Cutting off wavelengthsnot longer than 300 nm from the light for exposure allows a reduction indiscoloration, degradation or yellowing.

The coating thickness of the liquid crystal mixture (the coatingthickness after the solvent is dried off in the case that the mixture isa solution) is preferably from about 2 to about 20 μm. A coatingthickness of less than 1 μm is not preferred, because such a thicknesscan keep a certain reflection band width but tend to allow the degree ofpolarization itself to be degraded. The coating thickness is preferablyatleast 2 μm, more preferably at least 3 μm. A coating thickness of morethan 20 μm is not preferred, because such a thickness cannot provide asignificant improvement in any of reflection band width and degree ofpolarization and can simply increase the cost. The coating thickness ispreferably at most 15 μm, more preferably at most 10 μm, still morepreferably at most 7 μm. The coating thickness of the liquid crystalmixture is from 2 to 10 μm, preferably from 3 to 7 μm, in a case wherecolor properties are important for the coverage of the entire visiblelight range.

In the process of forming an infrared ray-reflecting film havingselective reflection properties beyond the visible light range, thecoating thickness may be 10 μm or more such that necessary reflectionproperties can be sufficiently obtained up to the long-wavelength end ofan infrared range. This is because concerning the selective reflectionof the cholesteric liquid crystal, there is a direct proportionalitybetween the selective reflection wavelength and the helical pitch asshown by the above formula so that the pitch length should be increasedas the wavelength becomes longer. The thickness should be as large asseveral pitches in order to provide a sufficient selective reflectivity.

For example, roll coating, gravure coating, spin coating, bar coating,or the like may be used in the process of applying the mixture solutionto the alignment substrate. After the mixture solution is applied, thesolvent is removed so that a liquid crystal layer can be formed on thesubstrate. The removal of the solvent may be performed under anyconditions, as long as the solvent can be almost removed without flowingor flowing down of the liquid crystal-layer. The solvent is usuallyremoved by drying at room temperature, drying in a drying oven, heatingon a hot plate, or the like.

Thereafter, the liquid crystal layer formed on the alignment substrateis heated to the isotropic transition temperature or higher to form aliquid crystal state of cholesteric orientation and then graduallycooled so that a uniform orientation state can be maintained. In thealignment process, the liquid crystal mixture is aligned in such amanner that the axis of the cholesteric spiral is aligned perpendicularto the surface of the alignment substrate.

For the alignment, the liquid crystal layer is heat-treated in theliquid crystal temperature range. The heat treatment method may be thesame as the above drying method. The heat treatment temperature varieswith the type of the liquid crystal material or the alignment substrateand cannot be uniquely defined, while it is generally from 60 to 300°C., preferably from 70 to 200° C. The heat treatment time varies withthe heat treatment temperature and the type of the liquid crystalmaterial or the alignment substrate used and cannot be uniquely defined,while it is generally selected from the range from 10 seconds to 2hours, preferably from 20 seconds to 30 minutes.

While the liquid crystal mixture maintains the aligned liquid crystalstate, ultraviolet irradiation is applied from the alignment substrateside to polymerize and cure the liquid crystal mixture. Ultravioletirradiation is applied to the liquid crystal mixture in such a statethat the mixture is in contact with an oxygen-containing gas.Ultraviolet irradiation is applied from the alignment substrate side sothat inhibition of polymerization by oxygen can be positively used.Thus, the polymerization is initiated from the alignment substratesurface side, and the progress of the polymerization is delayed at theside in contact with oxygen. In the production method, oxygen inhibitsthe polymerization so that the rate of the polymerization can be variedin the thickness direction, and thus the cholesteric pitch length of thecholesteric liquid crystal layer can be varied.

In the polymerization of the liquid crystal mixture, oxygen, whichbecomes a radical trap during the application of ultravioletirradiation, naturally diffuses from the coating surface side so thatthe concentration of the oxygen can vary in the thickness direction fromthe oxygen-supplying surface to the alignment substrate side. The rateof the polymerization can be varied depending on the concentration ofthe polymerization inhibitor, oxygen, so that the cholesteric pitchlength can be varied in the thickness direction.

The conventional techniques as disclosed in Japanese Patent ApplicationLaid-Open No. 06-281814 have many problems such as uneven thickness andan increase in the number of laminating steps caused by placement of acover film for preventing oxidative damages, and the additional cost ofthe cover film. In contrast, the production method of the inventionusing the oxygen inhibition can be free from such problems.

Ultraviolet irradiation may be applied under any conditions. Thecombination or control of the ultraviolet irradiation conditions and theheating conditions allows the production of the independent selectivereflection wavelength bands or modification of the distance between thecentral wavelengths of the selective reflection wavelength bands. In theprocess of exposure to ultraviolet irradiation, the environmentaltemperature may be raised in order to increase the mass-transfer speed.

In a case where a single step of applying ultraviolet irradiation isused for the polymerization, the temperature of the irradiation is atleast 20° C., preferably from about 30 to about 150° C. In this case,the intensity of ultraviolet irradiation is preferably from about 20 toabout 200 mW/cm², more preferably from 30 to 150 mW/cm². The ultravioletirradiation time may be from about 20 to about 120 seconds, preferablyfrom 25 to 60 seconds. If the intensity of Ultraviolet irradiation isless than 20 mW/cm², the polymerization in such a manner that adistribution of the monomer is formed in the thickness direction canfail to occur so that at least two independent selective reflectionwavelength bands can fail to be produced. If the intensity ofUltraviolet irradiation is more than 150 mW/cm², the rate of thepolymerization reaction can be higher than the rate of diffusion so thatat least two independent selective reflection wavelength bands can failto be produced.

Alternatively, the step of applying ultraviolet irradiation forpolymerization and curing may include an earlier stage and a later stagewhich are controlled such that the temperature of the irradiation ishigher at the later stage than at the earlier stage. The temperature ofthe irradiation at the earlier stage is preferably from about 20 toabout 100° C., more preferably from 30 to 50° C. At this stage, theintensity of ultraviolet irradiation is preferably from about 10 toabout 200 mW/cm², more preferably from 20 to 150 mW/cm², and theultraviolet irradiation time may be from about 0.2 to about 7 seconds,preferably from 0.3 to 5 seconds. If the intensity of ultravioletirradiation is less than 10 mW/cm², the polymerization in such a mannerthat a distribution of the monomer is formed in the thickness directioncan fail to occur so that at least two independent selective reflectionwavelength bands can fail to be produced. If the intensity ofultraviolet-irradiation is more than 200 mW/cm², the rate of thepolymerization reaction can be higher than the rate of diffusion so thatat least two independent selective reflection wavelength bands can failto be produced.

Only heat treatment may be performed before the irradiation at the laterstage. The heat treatment may be performed at a temperature of about 70to about 100° C. The heating time is preferably at least 2 seconds, morepreferably at least 10 seconds, generally from about 2 to about 120seconds.

The temperature of the irradiation at the later stage is preferably fromabout 60 to about 140° C., more preferably from 80 to 120° C. Within theabove ranges, the temperature difference between the earlier and laterstages is preferably at least 10° C., more preferably at least 20° C. Insuch a case, the intensity of ultraviolet irradiation is preferably fromabout 1 to about 20 mW/cm², and the UV irradiation time may be fromabout 10 to about 120 seconds, preferably from 10 to 60 seconds. If theintensity of ultraviolet irradiation is less than 1 mW/cm², thepolymerization in such a manner that a distribution of the monomer isformed in the thickness direction can fail to occur so that at least twoindependent selective reflection wavelength bands can fail to beproduced. If the intensity of ultraviolet irradiation is more than 20mW/cm², the rate of the polymerization reaction can be higher than therate of diffusion so that at least two independent selective reflectionwavelength bands can also fail to be produced.

In the environment during the ultraviolet irradiation, the liquidcrystal mixture applied to the alignment substrate is in contact with anoxygen-containing gas. The oxygen-containing gas preferably contains atleast 0.5% oxygen. Any environment capable of causing inhibition of thepolymerization by oxygen may be used, and the irradiation may beperformed under a usual air atmosphere. The oxygen concentration may beincreased or decreased in view of the wavelength width for pitch controlin the thickness direction and the velocity necessary for thepolymerization.

After the cholesteric liquid crystal layer is formed, the polymerizationmay be completed by intense ultraviolet irradiation. Such ultravioletirradiation is preferably performed in the absence of oxygen. Using suchultraviolet irradiation, curing can be achieved with no degradation ofthe cholesteric reflection bands, so that the pitch-varying structurecan be fixed without being degraded. Ultraviolet irradiation may beapplied from any of the alignment substrate side and the liquid crystalmixture coating side.

In the absence of oxygen, for example, an inert gas-atmosphere may beused. Any inert gas may be used, as long as it does not affect theultraviolet polymerization of the liquid crystal mixture. Examples ofsuch an inert gas include nitrogen, argon, helium, neon, xenon, andkrypton. In particular, nitrogen is most widely used and preferred.Alternatively, a transparent substrate may be attached to thecholesteric liquid crystal layer to provide oxygen-absent conditions.

Any ultraviolet irradiation conditions under which the liquid crystalmixture can be cured may be used. In general, ultraviolet irradiation ispreferably applied at a radiation intensity of about 40 to about 300mW/cm² for about 1 to about 60 seconds. The irradiation temperature maybe from about 20 to about 100° C.

The resulting cholesteric liquid crystal film may be used without beingseparated from the substrate or may be separated from the substratebefore use.

The cholesteric liquid crystal film of the invention has at least twofreely-selected independent selective reflection wavelength bands andhas the function of reflecting/transmitting circularly polarized lightin each of the selective reflection wavelength bands. The cholestericliquid crystal film of the invention may be used as acircularly-polarized-light-reflecting film.

A laminate may be provided which comprises two layers of thecircularly-polarized-light-reflecting films that have substantially thesame selective reflection wavelength bands and are opposite incholesteric twist direction. Such a laminate can function as areflecting film only for wavelengths in the two freely-selectedselective reflection wavelength bands.

A laminate similarly serving as a reflecting film may also be providedwhich comprises a laminate of two layers of the circularlypolarized-light-reflecting films that have substantially the sameselective reflection wavelength bands and are same in cholesteric twistdirection; and a half-wave plate placed between thecircularly-polarized-light-reflecting films.

While the half-wave plate may comprise any material, it is preferablyproduced with a general-purpose transparent resin film capable of havingretardation by stretching, such as a polycarbonate film, a polyethyleneterephthalate film, a polystyrene film, a polysulfone film, a polyvinylalcohol film, and a poly methyl methacrylate film; a norbornene resinfilm such as an ARTON film manufactured by JSR Corporation; or the like.Biaxial stretching may also be performed. In such a case, a retardationplate capable of compensating variations in retardation value dependingon the angle of incidence can be preferably used so that the view anglecharacteristics can be improved. Alternatively to the production of theretardation effect by stretching resins, for example, the half-waveplate may be produced by aligning a liquid crystal and fixing theresulting half-wave layer. Such a half-wave plate may also be used.Concerning the half-wave retardation, the front retardation value ispreferably within the range of about λ/2±40 nm, more preferably ofλ/2±15 nm, for light with a wavelength of 550 nm.

In such a cage, the thickness of the half-wave plate can besignificantly reduced. For example, the retardation plate produced bythe liquid crystal alignment has a thickness of several micrometers,while that produced by stretching has a thickness of several tens ofmicrometers.

In general, the thickness of the half-wave plate is preferably from 0.5to 200 μm, particularly preferably from 1 to 100 μm.

Single-material, single-layer half-wave plates can work well for aspecific wavelength but can sometimes have a degraded function for otherwavelengths due to their wavelength dispersion characteristics. Thus, atleast two types of different retardation plates each with a specifiedaxis angle and a specified retardation may be laminated. The resultinglaminate can be used as a broadband half-wave plate, which can work at apractically acceptable level in both of the two selective reflectionwavelength bands. In this case, the respective retardation plates may bemade of the same material, or the retardation plates may be producedwith different materials respectively, by the same method as for theabove half-wave plate and then combined. Such a broadband half-waveplate is particularly effective, if the space between the centralwavelengths of the two selective reflection wavelength bands is large,specifically if the selective-reflection wavelength band exists in eachof an ultraviolet wavelength range and an infrared wavelength range.

The cholesteric liquid crystal film (thecircularly-polarized-light-reflecting film) may have the centralwavelengths of the independent selective reflection wavelength bands inan ultraviolet wavelength range and an infrared wavelength range,respectively. The reflecting film comprising such a cholestericliquid-crystal film is useful as an eye protecting film. The reflectingfilm bonded to a transparent supporting substrate can be used as an eyeprotecting plate. The substrate used for producing the cholestericliquid crystal film may be used, as it is, as the transparent supportingsubstrate. Alternatively, any other similar substrate may be laminatedto form the transparent supporting substrate.

Damages to the eyes from ultraviolet irradiation include damages to thecornea (snow blindness), cloudiness of the lens (cataract), and retinaldamages (photoretinopathy). Such damages are not due to heat of lightbut due to photochemical reaction, and the degree of damages varies withthe wavelength band of the light radiation and the irradiation time. Itis known that in irradiation at short wavelengths within a visible rangefrom blue to violet, additivity exists between the light exposure andthe time, at a certain exposure dose that is from about one-millionsthto about ten-thousandth of the threshold for the thermal damages. Thatis described in detail in W. D. Gibbons and R. G. Alien: InvestOphthalmol. Visual Sci., 19, p. 521 (1977) and D. H. Sliney: OcularRadiation Hazards, Ch. 15 in Handbook of Optics III (2nd Ed.) pp.15.1-15.16. Concerning infrared rays, damages to the cornea aregenerally known, which are described in detail in D. Sliney and M.Wolbarsht: Safety with Lasers and Other Optical Sources, Pienμm Pr.(1980).

The eye protecting film or the eye protecting plate may be applied to avariety of transparent viewing members. For example, that may be used asan eye-protecting optical filter for spectacles or glasses includingsunglasses, protective glasses for laser working, and the like. That isalso preferably used for window-glasses of vehicle's such asautomobiles, windowpanes of buildings and the like.

A reflecting layer may be produced so as to cover two wavelengths withinthe visible light range. Such a reflecting layer can function as acomplementary color type reflecting filter, which can provide higherlight use efficiency and brighter display than a subtractive colorfilter or the like. The filter having such characteristics is preferablyused as a color filter for liquid crystal displays.

EXAMPLES

The invention is further described by means of the Examples andComparative Examples below, which are not intended to limit the scope ofthe invention.

(Reflectance Spectrum and Width of Selective Reflection Wavelength Band)

The reflectance spectrum of the cholesteric liquid crystal film wasmeasured with a spectrophotometer (Instantaneous Multisystem MCPD-2000manufactured by Otsuka Electronics Co., Ltd.), and a wavelength bandhaving at least half of the maximum reflectivity was defined as thewidth of the selective reflection wavelength band. The centralwavelength for selective reflection is a value at the middle of theselective reflection wavelength band.

The other measuring instruments included a spectrophotometer U4100manufactured by Hitachi, Ltd. which was used to measure spectralcharacteristics of transmission and reflection.

A front retardation value: (nx−ny)d and a thickness-directionretardation value: (nx−nz)d were calculated from the thickness d(nm) ofthe retardation layer and the refractive indexes nx, ny and nz at 550nm, which were measured with an automatic birefringence analyzer(KOBRA-21ADH manufactured by Oji Scientific Instruments), wherein nx isa refractive index in the direction of X-axis where the in-planerefractive index was maximum, ny is a refractive index in the directionof Y-axis perpendicular to X-axis, and nz is a refractive index in thedirection of Z-axis which was the direction of the thickness of thefilm. Retardations at oblique angles can be measured with the aboveautomatic birefringence analyzer. The Nz coefficient is defined by theformula: Nz=(nx−nz)/(nx−ny).

The ultraviolet exposure equipment used was UVC-321 AMI manufactured byUshio Inc.

Example 1

In a solvent (cyclopentanone) were dissolved 94.9 parts by weight of aphoto-polymerizable mesogen compound (1) (a polymerizable nematic liquidcrystal monomer) and 5.1 parts by weight of a polymerizable chiral agent(LC756 manufactured by BASF Ltd.). To the resulting solution was added0.5% by weight of a photopolymerization initiator (Irgacure 907manufactured by Ciba Specialty Chemicals Inc.), based on the solidscontent of the solution, so that a coating liquid (with a solids contentof 30% by weight) was prepared. The coating liquid was applied to astretched polyethylene terephthalate film (an alignment substrate) witha wire bar so as to provide a post-drying coating thickness of 5 μm, andthen the solvent was dried off at 100° C. for 2 minutes.

The resulting film was exposed to ultraviolet irradiation at 50 mW/cm²from the alignment substrate side at 85° C. under air atmosphere for 30seconds so that a cholesteric liquid crystal film was obtained which hadcentral wavelengths at 370 nm and 800 nm for selective reflection.Ultraviolet irradiation at 80 mW/cm² was then applied from the alignmentsubstrate side under a nitrogen atmosphere for 30 seconds so that thepolymerization was completed. During this ultraviolet irradiation, thecentral wavelengths for selective reflection were not changed. Thereflectance spectrum of the resulting cholesteric liquid crystal film isshown in FIG. 1.

Using a transparent pressure-sensitive adhesive (No. 7 manufactured byNitto Denko Corporation, 25 μm in thickness), the liquid ctystal side ofthe resulting cholesteric liquid crystal film was attached to each ofboth sides of a λ/2 plate (with a front retardation value of 270 nm),which was produced by uniaxially stretching a polycarbonate film, andthen the alignment substrate was separated so that atwo-wavelength-range reflection type reflecting film was obtained. Thereflecting film had two selective reflection wavelength bands in whichone central wavelength for selective reflection was 370 nm with a bandwidth of 75 nm and the other central wavelength for selective reflectionwas 850 nm with a band width of 170 nm.

Example 2

In a solvent (cyclopentanone) were dissolved 94.9 parts by weight of thephoto-polymerizable mesogen compound (1) and 5.1 parts by weight of apolymerizable chiral agent (LC756 manufactured by BASF Ltd.). To theresulting solution was added 0.5% by weight of a photopolymerizationinitiator (Irgacure 907 manufactured by Ciba Specialty Chemicals Inc.),based on the solids content of the solution, so that a coating liquid(with a solids content of 30% by weight) was prepared. The coatingliquid was applied to a stretched polyethylene terephthalate film (analignment substrate) with a wire bar so as to provide a post-dryingcoating thickness of 5 μm, and then the solvent was dried off at 100° C.for 2 minutes.

The resulting film was subjected to first exposure to ultravioletirradiation at 10 mW/cm² from the alignment substrate side at 40° C.under air atmosphere for one second. The film was then heated at 90° C.for one minute without ultraviolet irradiation. The film was thensubjected to second exposure to ultraviolet irradiation at 5 mW/cm² fromthe alignment substrate side at 90° C. under air atmosphere for 60seconds so that a cholesteric liquid crystal film was produced which hadcentral wavelengths at 370 nm and 800 nm for selective reflection.Ultraviolet irradiation at 80 mW/cm² was then applied from the alignmentsubstrate side under a nitrogen atmosphere for 30 seconds so that thepolymerization was completed. During this ultraviolet irradiation, thecentral wavelengths for selective reflection were not changed. Thereflectance spectrum of the resulting cholesteric liquid crystal film isshown in FIG. 2.

Using a transparent pressure-sensitive adhesive (Ad249 manufactured byTOKUSHIKI Co., Ltd., 5 μm in thickness), the liquid crystal side of theresulting cholesteric liquid crystal film was attached to each of bothsides of an NRZ film manufactured by Nitto Denko Corporation (with afront retardation value of 270 nm and an Nz coefficient of 0.5), andthen the alignment substrate was separated so that atwo-wavelength-range reflection type reflecting film was obtained. Thereflecting film had two selective reflection wavelength bands in whichone central wavelength for selective reflection was 405 nm with a bandwidth of 75 nm and the other central wavelength for selective reflectionwas 880 nm with a band width of 150 nm.

Comparative Example 1

In a solvent (cyclopentanone) were mixed and dissolved 93.5 parts byweight of the polymerizable mesogen compound (1) and 6.5 parts by weightof a polymerizable chiral agent (LC756 manufactured by BASF Ltd.) so asto provide a central wavelength of 370 nm for selective reflection. Tothe resulting solution was added 0.5% by weight of a photopolymerizationinitiator (Irgacure 907 manufactured by Ciba Specialty Chemicals Inc.),based on the solids content of the solution, so that a coating liquid(with a solids content of 30% by weight) was prepared.

In a solvent (cyclopentanone) were mixed and dissolved 96.5 parts byweight of the photo-polymerizable mesogen compound (1) and 3.5 parts byweight of a polymerizable chiral agent (LC756 manufactured by BASF Ltd.)so as to provide a central wavelength of 800 nm for selectivereflection. To the resulting solution was added 0.5% by weight of aphotopolymerization initiator (Irgacure 907 manufactured by CibaSpecialty Chemicals Inc.), based on the solids content of the solution,so that a coating liquid (with a solids content of 30% by weight) wasprepared.

The two types of the coating liquids were each independently applied toa stretched polyethylene terephthalate film (an alignment substrate)with a wire bar so as to each provide a post-drying coating thickness of3 μm, and then the solvent was dried off at 100° C. for 2 minutes. Theresulting films were exposed to ultraviolet irradiation at 47.5 mW/cm²from the cholesteric liquid crystal side at 40° C. under air atmospherefor 10 seconds so that a cholesteric liquid crystal film (A) with acentral wavelength of 370 nm for selective reflection and a cholestericliquid crystal film (B) with a central wavelength of 800 nm forselective reflection were produced, respectively. Ultravioletirradiation at 80 mW/cm² was then applied from the cholesteric liquidcrystal side under a nitrogen atmosphere for 30 seconds so that thepolymerization was completed. During this UV irradiation, the centralwavelengths for selective reflection were not changed.

The cholesteric liquid crystal films (A) and (B) were transferred andlaminated with a transparent adhesive (Ad249 manufactured by TOKUSHIKICo., Ltd., 5 μm in thickness) to form a broadbandcircularly-polarized-light-reflecting polarizer. The resultingreflective polarizer had central wavelengths at 370 nm and 800 nm forselective reflection.

The product was stacked on each of both sides of a retardation platewhich was the same as used in Example 1 so that a two-wavelength-rangereflection type reflecting film was obtained. The thickness of theresulting film was equal to that in Example 1. In this ComparativeExample, however, the number of lamination processes was twice that inExample 1, and the productivity was lower than in Example 1. A reductionin yield also occurred due to foreign materials.

INDUSTRIAL APPLICABILITY

The cholesteric liquid crystal film of the invention is useful as acircularly-polarized-light-reflecting plate (a circular polarizationtype reflective polarizer) and has two specific wavelength bands. If thetwo specific wavelength bands exist in an ultraviolet wavelength rangeand an infrared wavelength range, respectively, it will be useful as afilm for eye protection. Such a film is preferably used for eyeglassessuch as sunglasses and protective glasses for laser working,window-glasses of vehicles such as automobiles, and windowpanes ofbuildings. When the two specific wavelength bands exist in the visiblewavelength range, it is preferably used as a complementary color typefilter or the like for liquid crystal displays.

1. A cholesteric liquid crystal film, consisting of: a single layer,which is a cholesteric liquid crystal film, formed by applying a liquidcrystal mixture containing a polymerizable mesogen compound (A) and apolymerizable chiral agent (B) to an alignment substrate, and applyingultraviolet irradiation to the mixture, wherein the cholesteric liquidcrystal film has at least two independent selective reflectionwavelength bands.
 2. The cholesteric liquid crystal film according toclaim 1, wherein the independent selective reflection wavelength bandshave central wavelengths for selective reflection in an ultravioletwavelength range and an infrared wavelength range, respectively.
 3. Thecholesteric liquid crystal film according to claim 1, wherein a reactionrate of the polymerizable mesogen compound (A) and the polymerizablechiral agent (B) is different, respectively.
 4. The cholesteric liquidcrystal film according to claim 1, wherein the number of polymerizablefunctional groups in the polymerizable chiral agent (B) is larger thanthose in the polymerizable mesogen compound (A).
 5. A method ofproducing the cholesteric liquid crystal film according to claim 1,comprising the steps of: applying a liquid crystal mixture containing(A) a polymerizable mesogen compound and (B) a polymerizable chiralagent to an alignment substrate; and applying ultraviolet irradiation tothe liquid crystal mixture from the alignment substrate side in such astate that the mixture is in contact with an oxygen-containing gas topolymerize and cure the mixture.
 6. The method according to claim 5,wherein the step of applying ultraviolet irradiation to polymerize andcure the mixture is performed at a temperature of 20° C. or more.
 7. Themethod according to claim 5, wherein, an ultraviolet irradiationtemperature at a later stage in the step of applying ultravioletirradiation to polymerize and cure is controlled higher than that at anearlier stage.
 8. A two-wavelength-range reflection typecircularly-polarized-light-reflecting film, comprising the cholestericliquid crystal film according to claim
 1. 9. A reflecting film capableof covering two wavelength ranges, comprising: a laminate of two piecesof the circularly-polarized-light-reflecting film according to claim 8,wherein the two pieces of the circularly-polarized-light-reflecting filmhave substantially the same selective reflection wavelength bands andare opposite in cholesteric twist direction.
 10. A reflecting filmcapable of covering two wavelength-ranges, comprising: a laminate of ahalf-wave plate sandwiched between two pieces of thecircularly-polarized-light-reflecting film according to claim 8, whereinthe two pieces of the circularly-polarized-light-reflecting film havesubstantially the same selective reflection wavelength bands and aresame in cholesteric twist direction.
 11. The reflecting film accordingto claim 10, the half-wave plate is a broadband half-wave platecomprising a laminate of at least two different retardation plates. 12.An eye protecting film, comprising the reflecting film capable ofcovering two wavelength-ranges according to claim
 9. 13. An eyeprotecting plate, comprising: a transparent supporting substrate; andthe eye protecting film according to claim 12 which is bonded to thesubstrate.
 14. A transparent viewing member, comprising the eyeprotecting film according to claim
 12. 15. A complementary color filter,comprising the reflecting film according to claim
 8. 16. A liquidcrystal display, comprising the complementary color filter according toclaim
 15. 17. A transparent viewing member, comprising the eyeprotecting plate according to claim 13.